There is a continuing need in medical practice and research, and in analytical and diagnostic procedures for rapid and accurate determinations of chemical and biological substances which are present in various fluids, such as biological fluids. For example, the presence of drugs, hormones, steroids, polypeptides, metabolites, toxins, viruses, microorganisms or nucleic acids in human or animal body fluids or tissues must be determined rapidly and accurately for effective research, diagnosis or treatment.
In approximately the last twenty years, a wide variety of analytical methods have been developed to detect the substances noted above. Generally, the state of the art has advanced to such a degree that analytical and diagnostic methods have become highly reliable and suitable for automation or for use with test kits which can be readily used in doctors' offices or at home. Most of such methods rely on what are known as "specific binding" reactions in which an unknown substance to be detected (known as a "ligand") reacts specifically and preferentially with a corresponding "receptor" molecule. Most well known specific binding reactions occur between immunoreactants such as antibodies and antigens (substances which produce an immunological response, that is the production of antibodies), but other specific binding reactions (such as between a sugar and lectin, avidin with biotin or hybridization of complementary nucleic acids) are also well known.
Methods in the art using specific binding reactions generally require that one or more or both of the reactants be immobilized on a solid substrate of some type so that unreacted (and generally water-soluble) reactants can be separated from the water-insoluble reaction product (often called a "complex"). In addition, such immobilized reactants can be used in affinity chromatography to remove a desired ligand from a mixture of biologically active materials.
Receptor molecules have thus been immobilized to advantage on particulate substrates such as polymeric particles, glass beads, animal and human erythrocytes, bacterial cells and other solid particles of various sizes. For example, carrier particles prepared from polymers having various surface reactive groups, such as epoxy, carboxy, amino, hydroxy and aldehyde, are described in U.S. Pat. Nos. 4,401,765 (Craig et al) and 4,480,042 (Craig et al).
Biologically active latex particles are described in U.S. Pat. No. 4,563,431 (Pauly et al) as having surface acetal groups which are converted to aldehyde groups for attachment of biologically active substances. The outer polymers are prepared from monomers having pendant acetals linked to the vinyl portion through amidoalkyl groups of 2-7 carbon atoms. The polymers described therein tend to be hydrophilic which is not best for preparing biological reagents because they may have considerable water solubility and thus not be useful as solid substrates in immunoassays.
Other fine particulate carriers are described in U.S. Pat. No. 4,552,633 (Kumakura et al) as having surface aldehyde groups provided by vinyl monomers such as croton aldehyde, acrolein, methacrolein and citral. These monomers are disadvantageous because they lack sufficient hydrophobicity such as that provided by styrene-type monomers. Being hydrophilic, the monomers described by Kumakura et al are unstable for long term storage in aqueous media.
There remains a need in the art to provide biologically active reagents which can be prepared quickly and conveniently and which are colloidally stable under various conditions of use.
Previous aldehyde monomers suffer from the problem of water-solubility and when polymerized, especially using emulsion polymerization techniques, they form water soluble homopolymers and copolymers which contaminate the aqueous phase of the latex. Additionally, such hydrophilic monomers will not readily copolymerize with desired hydrophobic monomers such as styrene and styrene derivatives.